This invention relates generally to power supplies used in electronic systems. More particularly, this invention relates to a redundant power supply system with improved reference voltage sampling during low loads.
FIG. 1 illustrates an electronic system 20 with redundant power supplies. The system 20 includes a first power supply 22 and a second power supply 24 connected to a common power bus 25 that supplies power to a variable load 26. By way of example, the electronic system 20 may be a motherboard with a set of slots that form the variable load 26.
The first power supply 22 has a first power supply output node 28 connected to the common power bus 25 via a first power line 30. A first power line diode 32 is positioned on the first power line 30. The first power line diode 32 operates as an isolating diode so that the first power supply does not fight the second power supply 24.
The first power supply 22 also has a first sense line node 36 connected to the common power bus 25 via a first sense line 38. The first sense line 38 includes a first sense line diode 40 to create an isolated sense line.
The second power supply 24 has an identical configuration, including a second power supply output node 50 connected to the common power bus 25 via a second power line 52. A second power line diode 54 is positioned on the second power line 52. In addition, the second power supply 24 has a second sense line node 56 connected to the common power bus 25 via a second sense line 58. A second sense line diode 60 is connected to the second sense line 58.
The problems associated with the prior art electronic system 20 will be discussed in connection with the first power supply 22 with the understanding that the second power supply 22 has the same problems. When the first power supply 22 generates an output voltage at the first power supply output node 28, the output voltage experience a small voltage drop as a result of the first power line diode 32. The first sense line 38 has a high impedance. Therefore, at low loads the first sense line 38 does not draw any current. As a result, the first sense line diode 40 does not operate in its linear region, meaning that it does not measure small variations in voltage at low loads. This results in inaccurate output voltages from the first power supply 22. In addition, the output voltages are unstable since they are not accurately responding to the actual conditions within the electronic system 20. In order to measure small voltage variations at low loads, it is necessary to have the first sense line diode 40 operate in its linear region so that the sense node 36 of the power supply 22 can measure small voltage variations.
In view of the foregoing, it would be highly desirable to provide improved reference voltage sampling in electronic systems with redundant power supplies serving a small load. Improved reference voltage sampling would facilitate stabile and accurate output voltages at low loads.
An embodiment of the invention includes an electronic system with a common power bus and a load connected to the common power bus. A first power supply output node and a first sense line node of a first power supply are connected to the common power bus. A second power supply output node and a second sense line node of a second power supply are connected to the common power bus. A sense line load adjustment circuit is linked to the common power bus, the first sense line node, and the second sense line node. The sense line load adjustment circuit is configured to generate a mirror voltage that provides a corrected reference voltage at the first sense line node and the second sense line node in the presence of a relatively small load.
Another embodiment of the invention includes an electronic system with a common power bus and a load connected to the common power bus. A first power supply has a first power supply output node and a first sense line node. A first power line is connected between the first power supply output node and the common power bus. A first power line diode is positioned on the first power line. A first sense line is connected between the first sense line node and the common power bus. A first sense line diode is positioned on the first sense line. A second power supply has a second power supply output node and a second sense line node. A second power line is connected between the second power supply output node and the common power bus. A second power line diode is positioned on the second power line. A second sense line is connected between the second sense line node and the common power bus. A second sense line diode is positioned on the second sense line. A sense line load adjustment circuit is connected to the first sense line and the second sense line. The sense line load adjustment circuit generates a control current to place the first sense line diode and the second sense line diode in a linear region of operation in the presence of a relatively small load.
The invention provides improved reference voltage sampling in electronic systems with redundant power supplies serving low loads. Improved reference voltage sampling stabilizes the output voltages generated by the redundant power supplies. Thus, the redundant power supplies provide more accurate output voltages to isolated sense lines, particularly at low loads. Advantageously, the invention can be implemented using low cost components and simple manufacturing techniques.